From f8bc3ffc22ab91366426a2545898cbc42d4c70bb Mon Sep 17 00:00:00 2001
From: Marek Safar <marek.safar@gmail.com>
Date: Fri, 21 Dec 2018 20:15:08 +0100
Subject: [PATCH] Moves ByReference to shared CoreLib (dotnet/coreclr#21633)

Signed-off-by: dotnet-bot <dotnet-bot@microsoft.com>
---
 .../System.Private.CoreLib.Shared.projitems   |  1 +
 .../shared/System/ByReference.cs              | 42 +++++++++++++++++++
 2 files changed, 43 insertions(+)
 create mode 100644 netcore/System.Private.CoreLib/shared/System/ByReference.cs

diff --git a/netcore/System.Private.CoreLib/shared/System.Private.CoreLib.Shared.projitems b/netcore/System.Private.CoreLib/shared/System.Private.CoreLib.Shared.projitems
index 0c40e26e9c66..27d43b76f8d2 100644
--- a/netcore/System.Private.CoreLib/shared/System.Private.CoreLib.Shared.projitems
+++ b/netcore/System.Private.CoreLib/shared/System.Private.CoreLib.Shared.projitems
@@ -111,6 +111,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Buffers\Text\Utf8Parser\Utf8Parser.TimeSpan.LittleG.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Buffers\Text\Utf8Parser\Utf8Parser.TimeSpanSplitter.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Byte.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\ByReference.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Char.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\CharEnumerator.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\CLSCompliantAttribute.cs" />
diff --git a/netcore/System.Private.CoreLib/shared/System/ByReference.cs b/netcore/System.Private.CoreLib/shared/System/ByReference.cs
new file mode 100644
index 000000000000..492979a2d75b
--- /dev/null
+++ b/netcore/System.Private.CoreLib/shared/System/ByReference.cs
@@ -0,0 +1,42 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Runtime.CompilerServices;
+using System.Runtime.Versioning;
+
+namespace System
+{
+    // ByReference<T> is meant to be used to represent "ref T" fields. It is working
+    // around lack of first class support for byref fields in C# and IL. The JIT and 
+    // type loader has special handling for it that turns it into a thin wrapper around ref T.
+    [NonVersionable]
+    internal readonly ref struct ByReference<T>
+    {
+        // CS0169: The private field '{blah}' is never used
+#pragma warning disable 169
+         private readonly IntPtr _value;
+#pragma warning restore
+
+        [Intrinsic]
+        public ByReference(ref T value)
+        {
+            // Implemented as a JIT intrinsic - This default implementation is for 
+            // completeness and to provide a concrete error if called via reflection
+            // or if intrinsic is missed.
+            throw new PlatformNotSupportedException();
+        }
+
+        public ref T Value
+        {
+            [Intrinsic]
+            get
+            {
+                // Implemented as a JIT intrinsic - This default implementation is for 
+                // completeness and to provide a concrete error if called via reflection
+                // or if the intrinsic is missed.
+                throw new PlatformNotSupportedException();
+            }
+        }
+    }
+}